Allison HT740 transmission

What vehicle does the above transmission fit?

[HR][/HR]

More info here....


G.

Anything with an SAE #1 flywheel that put out 445HP or less at 1400ft-lbs or less peak torque. Really common in the private sector too - my Bus has one.

One thing to watch for - the lock-up clutch on the military version is aggressive, this is why they had to put anti-lock brakes in the M939 series trucks. Guys were stomping on the brakes and the lock-up clutch wouldn't release, killing the engine and thus the power steering.

[Edit:] Should note, the lock-up clutch is accessible via a hydraulic port - you can add a solenoid valve and make the lock-up clutch controllable. I have a full factory service manual if you have any questions [/Edit]

Thanks for the information. I have been looking for a spare MT654CR trans "just in case" ours goes out in the future. I wonder what it would take to modify the HT740 trans to fit our M923a2 trucks.

This tripped me the heck out since I was just writing a post in this thread discussing Allison Automatic options for an ISX swap - got my thread mixed up (where's the post I just did!!).

In general, it's my belief that the MT654 and HT740 share the external case part, so I think (check the measurements yourself) the HT740 should just be a drop in. There will probably be a few parts you'd have to transfer over (modulator input, shifter) but other than that it should be stupid easy . These were designed around SAE standardized mounting fixtures and package sizes - once you go bigger than a pickup-truck, it actually gets easier to mix and match.

Do you have the transmission already?

I won a few just waiting for the euc to clear and then have them shipped to me.

Suprman said:

I won a few just waiting for the euc to clear and then have them shipped to me.

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Agh OK, i have one as well in a crate that I will probably be selling, thanks

tim292stro said:

This tripped me the heck out since I was just writing a post in this thread discussing Allison Automatic options for an ISX swap - got my thread mixed up (where's the post I just did!!).

In general, it's my belief that the MT654 and HT740 share the external case part, so I think (check the measurements yourself) the HT740 should just be a drop in. There will probably be a few parts you'd have to transfer over (modulator input, shifter) but other than that it should be stupid easy . These were designed around SAE standardized mounting fixtures and package sizes - once you go bigger than a pickup-truck, it actually gets easier to mix and match.

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Would the shifting points be any different? Also I have read a lot of threads on turning up the 6CTA8.3's and the weak points seem to be the trans and transfer cases, would a trans swap leave the transfer the sole weak point. I am thinking of bobbing a 923A2 and turning up the fuel but I would not be adding any cargo to it (heavy loads)! I would think the transfer could handle the extra power with a lot less weight. Please give me some in put.
Thanks Warren

The HT740 is a 4-speed auto. I believe the shift points in both transmissions are adjustable, to a point at least. The M939 trucks are geared low so you may loose some top end with the 740 trans. It is very popular in busses, motor homes, garbage trucks and other heavy vehicles. The HT750 is a 5 speed that may be a better choice for the 5 ton.
Will

At a top speed of 55 mph, I don't want to loose any more. lol...

My 936 will do 70. Why does yours only do 55?

Manual says 55 mph maximum speed. I don't know how fast it will go. I only have had it up to 50 mph so far.
Just brought home a M1101 tonight. Can't wait to see how it fits behind the M923a2.

My 936 with NHC250 & duels will do 60! My 923A2 with super singles will run very close to 70.

Mine does 60 duals

Suprman said:

The HT740 is a 4-speed auto. I believe the shift points in both transmissions are adjustable, to a point at least. The M939 trucks are geared low so you may loose some top end with the 740 trans. It is very popular in busses, motor homes, garbage trucks and other heavy vehicles. The HT750 is a 5 speed that may be a better choice for the 5 ton.
Will

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top end speed shouldn't change as the final gear in both units is 1:1/direct

The shift points in all of the Allison's are adjustable and need to be set to match the governed RPM of the engine. Unfortunately this requires removing the pan to do the adjustments and it is recommended to do it on a dyno and not in the truck.

There are also multiple torque converters available for each transmission.

The MT654CR transmission is considered obsolete by allison

Unfortunately most of the transmissions in the 939 series trucks are not set up to allison specifications.

quickfarms said:

The shift points in all of the

The MT654CR transmission is considered obsolete by allison

Unfortunately most of the transmissions in the 939 series trucks are not set up to allison specifications.

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Tell me about it. WAJAX an Allison/Detroit diesel service center told me the MT654CR was a mismatch transmission to a 6CTA engine when I was trying to get the valve body adjusted.

There's a reason the military killed the 939 series. AM General made the wining design but the government gave later production of that design to BMY-Harsco who did a really bad execution of design cost-reduction, kind of like Stewart&Stevenson with the LMTV drive-train design issues. Even ABS later was a band-aid rather than a fix of the bad engine/transmission pairing, an even more futile fix for the fatal roll-overs was the later "high-tops" with built in ROPS, which unfortunately only protects the in-cab crew, and not the equipment or soldiers in the back (so what's the point the military asked in summary?).



BMY-Harsco is not primarily in the business of building vehicles.
Stewart&Stevenson is not primarily in the business of building vehicles.

This mismatch and basic design screw-ups is what you get when companies are picked to build vehicles where they have no experience.